These rifling grooves were mostly cosmetic, as they did not really impart any spin to the slug at all as it went through the barrel. The only real purpose, other than making the customer "feel like" his slugs would spin, was to allow the slugs to be swedged through any size choke. The manufacturers of the slugs could not know for sure what choke would be used by the customer, so they put these grooves on the slugs to allow them to swedge through any normal choke.
We then must ask, "If the rifling does not spin the slug, then what causes the rifled slug to fly true?" The answer is that the slugs usually had a hollow base and they were heavier in the front than in the back, and flew straight for the same reason a dart flies true.
Some other types of rifled slugs, like Brenneke slugs, have a solid slug with a lighter-weight base that was attached to the slug. This method worked in the same manner.
But with the advent of rifled slug barrels, manufacturers developed a sabot type slug. (Sabot is pronounced "say-bow", and comes from the French word for shoe.)
A sabot slug has a solid slug encased in a removable sabot that will be spun by the rifling in the barrel and then separate from the slug after it leaves the barrel. The slug will continue on without the sabot and continue to spin for stabilization. This results in much more accuracy for the shooter of the sabot slugs.
But our question today is: Can these sabot slugs be effectively shot through a smooth bore shotgun?
Well, only one way to find out.
First, we will shoot some sabot slugs through a rifled barrel. My friend Vern has a Remington 11-87 with a rifled barrel and a scope. We will be shooting at 50 yards today.
Some folks use these shotguns for much longer shots, but this is a more reasonable range for best accuracy.